Physical and chemical dynamics of temporary ponds on a calcareous plateau in Thuringia, Germany     

Jens Arle   《Limnologica》2002,32(2)

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非均匀层结下的对称不稳定          下载免费PDF全文

张立凤  张铭 《大气科学》1997,21(5):627-632

研究了非均匀层结下的对称不稳定，给出了不稳定发生的判据，并将该微分方程的特征值问题化为一个实对称矩阵的特征值问题，还取不同的层结廓线进行了数值计算。  相似文献   

湖北省冻雨天气特征及其判定方法研究     

周悦  许冠宇  高正旭  杨加仑 《气象科技》2016,44(6):949-955

利用常规地面气象站多时次气象要素和天气现象观测资料,以及武汉、宜昌和恩施的探空资料,对1998—2014年湖北地区冻雨天气的主要环流背景进行了分析,归纳了冻雨发生发展过程的气象要素和大气层结特征,给出了基于正负能量面积的冻雨发生定量化判断方法。结果表明:乌山阻高型和贝湖阻高型是导致湖北省出现冻雨天气的两种主要天气形势;2005年和2月是冻雨主要发生的年份和月份;共存在3种典型的气温层结演变特征,其中"暖雨-冻雨-固态"的气温层结演变最易导致持续时间长、影响范围大的冻雨天气;基于正负能量面积的冻雨判定方法为:3层层结时,正能量面积(A_(SP))小于80℃·hPa,负能量面积(A_(SN))小于400℃·hPa,且正负能量关系为(5.71A_(SP)-257.14)≤A_(SN)≤(6.25A_(SP)+200);2层层结时,ASP为350~650℃·hPa,A_(SN)为200~400℃·hPa,且正负能量关系为(A_(SP)-350)≤A_(SN)≤(ASP-100)。  相似文献   

季节性冰封热融浅湖水温原位观测及其分层特征   总被引：1，自引：0，他引：1       下载免费PDF全文

黄文峰  韩红卫  牛富俊  李志军 《水科学进展》2016,27(2):280-289

为探究季节性冰封浅湖热力学特征,于2010年10月至2013年7月对高原腹地一典型热融湖塘冰层生消、水/冰温及气象条件开展原位观测,分析了水温分布时间变化、温跃层以及冰生消对水温结构的影响。结果发现:冰面升华显著,贯穿整个冰期;水温日变化、季节变化和垂直结构受气温、大气辐射、风速、冰生消和湖底沉积层热贡献影响显著;在"无冰期-结冰前-冰生长期-冰融化期-融化后-无冰期"年循环过程中水温垂直结构分别呈现出"分层-翻转-逆温分层-逆温与正温共存-翻转-分层"的循环过程。分层期水温结构仅由上部混合层和温跃层构成,且偶因强风搅动而全湖翻转混合。可见,相比大中型湖泊,季节性冰封浅湖热力学结构差异显著。  相似文献   

Characterization of hard‐to‐differentiate dune stratification types in the Permian Coconino Sandstone (Arizona,USA)     

Sarah A. Maithel  Leonard R. Brand  John H. Whitmore 《Sedimentology》2021,68(1):238-265

Dune stratification types, which include grainfall, grainflow and ripple lamination, provide a record of the fine‐scale processes that deposited sediment on palaeo‐dune foresets. While these facies are relatively easy to distinguish in some cross‐bedded sandstones, for others – like the Permian Coconino Sandstone of northern and central Arizona – discrete stratification styles are hard to recognize at the bedding scale. Furthermore, few attempts have been made to classify fine‐scale processes in this sandstone, despite its renown as a classic aeolian dune deposit and Grand Canyon formation. To interpret depositional processes in the Coconino Sandstone, cross‐bed facies were characterized using a suite of sedimentary textures and structures. Bedding parameters were described at multiple scales via a combination of field and laboratory methods, including annotated outcrop photomosaics, strike and dip measurements, sandstone disaggregation and laser‐diffraction particle analysis, high‐resolution scans of thin sections, and scanning electron microscopy. Cross‐beds were observed to be laterally extensive along‐strike, with most dip angles ranging from the mid‐teens to mid‐twenties. While some cross‐bed sets are statistically coarser near their bases, others exhibit no significant vertical sorting trends. Both massive and laminated textures are visible in high‐resolution scans of thin sections, but laminae contacts are commonly indistinct, making normal and reverse grading difficult to define. Diagenetic features, such as stylolite seams and large pores, are also present in some samples and might indicate alteration of original textures like detrital clay laminae and carbonate minerals. Observed textures and sedimentary structures suggest that the cross‐beds may consist of grainflow and grainfall deposits, but these remain difficult to differentiate at outcrop and thin‐section scales. This characterization of fine‐scale processes will play a critical part in the development of depositional models for the Coconino Sandstone and elucidate interpretations for similar cross‐bedded formations.  相似文献   

SEARCH FOR CORRELATIVITY OF LIGHTNING(STROKE)WITH ATMOSPHERIC STRATIFICATION FACTORS          下载免费PDF全文

Zhang Xixuan  Zhang Cuihua 《Acta Meteorologica Sinica》1991,5(2):252-252

In this paper the statistical analysis is carried out on the correlation between lightning strokes andatmospheric stratification factors.It is shown that the total number of strokes in lightning process is mainlydecided by environmental temperature at altitude with the residual instability of 5℃(T_r).The instabilityshould also affect the total number of strokc in lightning process.A forecasting equation of stroke in light-ning process has been deduced and two interesting preliminary conclusions have been obtained.  相似文献   

Parameterisation of the vertical transport in a small thermally stratified lake     

Christoph von Rohden  Karl Wunderle  Johann Ilmberger 《Aquatic Sciences - Research Across Boundaries》2007,69(1):129-137

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华北地块东段和龙超镁铁质科马提岩的发现及特征          下载免费PDF全文

刘劲鸿 《地质论评》2001,47(4):420-424

和龙岩体赋存于新太古代夹皮沟—金城洞花岗绿岩带中,与围岩发生同变形变质。岩体具有典型的科马提岩冷凝结构分层和鬣刺结构、冷凝多面体节理。上述特征是作者1990年发现确认的。该科马提岩的矿物学特征:玻璃质脱玻形成铁皂石等矿物;斜方辉石和橄榄石鬣刺呈中空骸晶状,大部被滑石、铁白云石、绿泥石、磁铁矿等取代,但仍保留完好的长柱状假像;堆积带中橄榄石呈微细粒、新鲜,仅发生网状蛇纹石化。岩石化学特征富MgO,CaO/Al_2O_3=1.04,用科马提岩分类图判别为超镁铁质科马提岩。  相似文献   

大陆岩石圈流变学研究   总被引：2，自引：1，他引：2  

索书田 《地质科技情报》1992,11(2):6-10

简单介绍了流变学的概念和两种基本研究方法,基于大陆岩石圈较大洋岩石圈有更为复杂的流变特征客观事实,指出研究大陆岩石圈流变学的重要性,并提出几个主要的研究方向和领域。  相似文献   

Permeability of stratified sands     

C. O. Okagbue 《Geotechnical and Geological Engineering》1995,13(3):157-168

Summary The permeability of graded sands was studied in the laboratory to determine the influence, if any, of stratification order on permeability (i.e. the position in which finer or coarser layers occur in the flow path). The evidence suggests that the order of stratification does not influence the order of magnitude of permeability of a sand. This order of magnitude is determined by the fine fraction of the sand. However, the order of stratification does have an influence on the finer details (i.e. variation within the same order of magnitude) of permeability. In this regard, an unsorted sand (all fractions mixed together) has the lowest permeability while a sorted one that has the fine fraction at the end of the sequence has the highest vertical permeability. It is also concluded that empirical formulae that use only the effective size, D ₁₀, to estimate permeability yield results that are comparable with those that incorporate sorting in their formulae. However, experimental results show that these formulae do not yield reliable results when used for more denser sands.  相似文献